1. Field of the Invention
The present invention relates to a fuel control apparatus for an internal combustion engine wherein a parameter related to an air intake quantity to be sucked into the internal combustion engine is detected by an air intake quantity detecting means and fuel supply to the engine is controlled based on the output of the air intake quantity detecting means.
3. Discussion of Backgrounds
In controlling fuel for internal combustion engine, an air flow sensor (hereinafter, referred to as AFS) is disposed at the upstream of a throttle valve so as to detect an air intake quantity to the engine, and an air intake quantity per one suction is obtained by the information of the AFS and the number of revolution of the engine, whereby the fuel quantity to the engine is the controlled.
In the above-mentioned system wherein the AFS is disposed in an air intake passage at the upstream side of the throttle valve to thereby detect an air intake quantity to the engine, however, when the throttle valve is rapidly opened, the AFS detects an amount of air filled in the intake passage between the throttle valve and the internal combustion engine, whereby the AFS detects an amount of air more than the air quantity sucked into the internal combustion engine. In the conventional fuel control apparatus, the following measures were taken in order to eliminate the above-mentioned disadvantage. Namely, an air intake quantity per one suction was subjected to a filter treatment to thereby obtain a correct value of air intake quantity to be sucked into the internal combustion engine. Further, a delay in the filtering treatment and a delay in an air intake quantity detection output were corrected. In addition, correction of an incremental value was conducted in order to compensate a shortage of the fuel supply quantity at the time of acceleration of the engine when a change of the output by the filter treatment is a predetermined value or higher. Thus, the fuel control at a transition period was appropriately conducted.
The filter treatment is conducted on the basis of the formula described below, for instance. EQU AN.sub.(n) =K.sub.1 .times.AN.sub.(n-1) +K.sub.2 .times.AN.sub.(t)
where AN.sub.(t) an air intake quantity obtained on the basis of an output from the AFS between predetermined crank angles in the internal combustion engine, AN.sub.(n-1) : a sucked air intake quantity which has undergone a filter treatment at the last time, AN.sub.(n) : a sucked air intake quantity which has undergone the filter treatment at the present time, and K.sub.1, K.sub.2 : constants (where K.sub.1 +K.sub.2 =1)
In the above-mentioned formula, it is necessary to change the value of constants (K.sub.1, K.sub.2) for the filter treatment depending on operational conditions of the internal combustion engine. For instance, when the engine is in an idling operation, a change of revolution speed in an idling time can be reduced by reducing the constant K.sub.1 to be smaller than an appropriate value. At this moment, however, a degree of variability in the value of air intake quantity which has been subjected to a filter treatment becomes large, whereby correction of the incremental value has to be carried out even in a time other than the transition period.